Sensing small magnetic fields by great magnetoresistance changes, with little chip area consumption and little manufacturing process complexity, is increasing in importance in applications in automobile and industrial electronics. Thus, it is particularly important to achieve compatibility and optimization of parameter swing or signal swing (magnetoresistance change in dependence on a magnetic field change), chip area, manufacturing process complexity, current consumption etc.
Presently, GMR (giant magnetoresistance) structures and TMR structures or TMR layer systems are employed in sensor technology. In electrical contacting, a distinction is made between a CIP configuration and a CPP (current perpendicular to plane) configuration. In the CIP configuration, the layer system is contacted from one side and the current flows parallel to the layer system, whereas in the CPP configuration the layer system is contacted from two sides so that the current flows perpendicular to the layer system. GMR layer systems are typically operated in the CIP configuration, which entails comparatively little process complexity due to contacting being required from only one side to a layer package or layer structure. However, the signal swing, i.e. a resistance change as a consequence of a change in the magnetic field to be sensed and, in particular, a change in the orientation of the magnetic measuring field relative to a reference magnetic field, in GMR layer systems, such as, for example, in so-called spin-valve systems, is presently limited to 10-20%. Greater sensitivity would be desirable for further improvement of characteristics of magnetoresistive sensors and for extending the fields of application. Additionally, a disadvantageous temperature stability of GMR systems is the result of a potential diffusion behavior of materials, such as, for example, copper.
On the other hand, resistance changes of more than 200% are at present measured in TMR structures or layer systems, which are thus more sensitive than GMR structures or GMR layer systems by a factor 20. However, the CPP configuration is used for achieving a maximum effect quantity (signal swing) requiring contacting the layer package or layer system from two sides. Compared to GMR contactings, this entails increased process and cost complexity, since at least one additional metallization level is necessary.
Thus, it would be desirable to find a way of achieving a considerable increase in the signal swing when maintaining the relatively simple and technically controllable CIP contacting, like in a GMR process.